Spatial light modulators (SLMs) have numerous potential technical applications such as multispectral infrared target simulation, projection television systems, and optical computer systems. First introduced by Preston in 1968, deformable membrane mirror light modulators (MLMs), which incorporate a highly reflective membrane as the light modulating element, have generated interest within the applied optics community as good candidates for both adaptive optics and projection display applications. Various means of addressing the two-dimensional deformable membrane mirror have been demonstrated, including electron beam-addressing, optical addressing, and electrical addressing via integrated circuits. These devices have not progressed beyond the development state, hence there are no MLMs on the commercial market. The electron beam-addressed approach is preferred for display applications due to the high resolution and convenience of direct video addressing; however, development of suitable substrates which would decouple the electron beam interaction region from the reflective mirror were lacking. One method of solving this problem is by introducing the charge-transfer plate (CTP) as a means of providing both structural integrity and electrical signal transfer to the mirror elements. This approach has improved the state-of-the-art by yielding a device with a large number of resolution elements, high contrast, and low voltage operation. (see U.S. Pat. No. 4,794,296 assigned to the assignee of this application)
Such a system is shown in FIG. 18 of the above referenced '296 patent and is more particularly described on column 15, lines 21 through 38 thereof. The charge transfer plate creates a two-dimensional electric field which produces a local displacement of the metalized reflective membrane to provide local modulation of the phase output of the two-dimensional light signal reflected from the mirror. These SLMs exhibit very fast response times, can be read out with high optical efficiency, and in principle can incorporate a very large number of resolution elements. Since a deformable mirror SLM is essentially a two-dimensional phase modulating element with a large phase dynamic range, it is well-suited to adaptive optics applications such as wavefront correction, laser beam steering and phase only spatial filtering. With appropriate pixelization of the membrane surface, intensity modulation may be accomplished via the schlieren readout schemes employed by projection display systems such as the Eidophor (G.E.) and the .gamma.-Ruticon (Xerox).
Recent improvements in the MLM and the system for modulating the charge thereon have involved a MLM wherein a membrane is deposited over an array of wells with an addressable electrode at the bottom of each well. Thus, the well and its electrode define an individual pixel. The membrane is coated with a thin light reflecting electrode material held at a static potential. A pixel is activated by establishing a potential difference between the well electrode and the membrane electrode, causing the membrane to deform into the well region in response to electrostatic forces. Hence, the pixel driving voltage induces a local phase modulation on the readout wavefront reflected by the membrane mirror surface. Such a system is described in "Electron Beam Addressed Membrane Light Modulator", Spatial Light Modulators and Applications, 1990 Technical Digest Series, Vol. 14, Optical Society of America, Sept. 1990.